Method and apparatus for changing operating mode in wireless LAN system

ABSTRACT

The present specification proposes a signal processing method for changing an operating mode for transmitting a PPDU in a wireless LAN system. Specifically, a first station receives, from the second station, indication information which indicates a change in an operating mode indicating a receiving channel bandwidth and a number of spatial streams supported by a second station during a TXOP interval. When the number of spatial streams and the receiving channel bandwidth decrease, the first station configures a PPDU for the second station by using the indication information after transmitting an ACK for the indication information. When the number of spatial streams and the receiving channel bandwidth increase, the first station configures a PPDU for the second station by using the indication information during a subsequent TXOP interval of the TXOP interval.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2017/003673, filed on Apr. 4, 2017,which claims the benefit of U.S. Provisional Applications No.62/331,982, filed on May 5, 2016, 62/333,884, filed on May 10, 2016,62/360,972, filed on Jul. 12, 2016 and 62/363,323, filed on Jul. 17,2016, the contents of which are all hereby incorporated by referenceherein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

This specification relates to a method associated with an operating modein a wireless local area network (LAN) system and, most particularly, toa method and apparatus for changing an operating mode during apredetermined time period (or time interval) in a wireless station of awireless LAN system.

Related Art

Discussion for a next-generation wireless local area network (WLAN) isin progress. In the next-generation WLAN, an object is to 1) improve aninstitute of electronic and electronics engineers (IEEE) 802.11 physical(PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHzand 5 GHz, 2) increase spectrum efficiency and area throughput, 3)improve performance in actual indoor and outdoor environments such as anenvironment in which an interference source exists, a denseheterogeneous network environment, and an environment in which a highuser load exists, and the like.

An environment which is primarily considered in the next-generation WLANis a dense environment in which access points (APs) and stations (STAs)are a lot and under the dense environment, improvement of the spectrumefficiency and the area throughput is discussed. Further, in thenext-generation WLAN, in addition to the indoor environment, in theoutdoor environment which is not considerably considered in the existingWLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned in thenext-generation WLAN and discussion about improvement of systemperformance in a dense environment in which the APs and the STAs are alot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are anticipatedto be actively discussed rather than improvement of single linkperformance in one basic service set (BSS). Directionality of thenext-generation means that the next-generation WLAN gradually has atechnical scope similar to mobile communication. When a situation isconsidered, in which the mobile communication and the WLAN technologyhave been discussed in a small cell and a direct-to-direct (D2D)communication area in recent years, technical and business convergenceof the next-generation WLAN and the mobile communication is predicted tobe further active.

SUMMARY OF THE INVENTION

This specification proposes an enhanced field structure and an enhancedsignaling method associated with the operating mode.

This specification proposes an example of the operating mode beingchanged at a predetermined time in transmitting and receivingapparatuses according to the present invention. Additionally, thisspecification proposes diverse examples related to UL MU transmissionthat is associated with the operating mode.

This specification proposes an example related to a method of processingcontrol information for configuring a physical layer protocol data unit(PPDU) in a wireless LAN system and an apparatus performing thecorresponding method.

First, terms used herein are defined as follows. A first station (STA)may correspond to an access point (AP) STA, and a second STA maycorrespond to a non-AP STA that performs communication with the AP STA.

The first STA receives, from the second STA, indication information thatindicates a change of an operating mode indicating the number of spatialstreams and a receiving channel bandwidth supported by the second STAduring a transmission opportunity (TXOP) interval. That is, since theindication information that indicates the change of the operating modemay correspond to a receive operating mode (ROM) request, the second.STA makes an ROM change request to the first STA. The receiving channelbandwidth may include at least one of 20 MHz, 40 MHz, 80 MHz, and 160MHz.

When the number of spatial streams and the receiving channel bandwidthare reduced, the first STA configures a PPDU for the second STA usingthe indication information after transmitting an ACK of the indicationinformation. Further, when the number of spatial streams and thereceiving channel bandwidth are reduced, the PPDU for the second STA maybe configured during the TXOP interval or a TXOP interval subsequent tothe TXOP interval. That is, once the ACK of the ROM request istransmitted to the second STA, a changed ROM may be applied even in thecurrent TXOP interval.

When the number of spatial streams and the receiving channel bandwidthare increased, the first STA configures a PPDU for the second STA usingthe indication information during a TXOP interval subsequent to the TXOPinterval. Further, when the number of spatial streams and the receivingchannel bandwidth are increased, the PPDU for the second STA may beconfigured during the TXOP interval subsequent to the TXOP intervalregardless of transmitting the ACK of the indication information.

The indication information may include an operating mode changeindicator bit. The operating mode change indicator bit may correspond toan ROM change indicator hit. The operating mode change indicator bit mayindicate a TXOP interval in which the PPDU for the second STA isconfigured. That is, an interval in which an ROM change is applied maybe identified on the basis of a value indicated by the operating modechange indicator bit.

The indication information may be included in a data field of a PPDUforwarded to the first STA. The data field of the PPDU forwarded to thefirst STA may correspond to a QoS data frame. Further, the indicationinformation may be included in a medium access control (MAC) header ofthe data field.

The indication information may indicate whether the second STA indicatesuplink multi-user (UI. MU) transmission, the number of receiving spatialstreams supported by the second STA, and the number of transmittingspatial streams supported by the second STA. That is, the indicationinformation may be used as information on a transmit operating mode whenthe second STA performs UL MU communication through a trigger frame.

According to an example of this specification, the operating mode oftransmission and reception apparatuses may be changed at a preset time.Further, an improved field structure and an improved signaling schemerelated to the operating mode may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a sub-field included in a per userinformation field.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field.

FIG. 12 illustrates an example of control information 1200 used toreport an operating mode.

FIG. 13 illustrates an example of the reported operating mode being usedfor UL MU operations.

FIG. 14 illustrates an example of the reported operating mode being usedfor receiving operations of a specific STA.

FIG. 15 illustrates an additional example of the reported operating modebeing used for the receiving operations of a specific STA.

FIG. 16 illustrates an example of a BA frame for a plurality of STAs.

FIG. 17 illustrates an example of an Aggregated-Control (A-Control)field used to transfer control information.

FIG. 18 illustrates an example in which disagreement in operating modeoccurs between an AP and an STA.

FIG. 19 illustrates an example in which disagreement in operating modeoccurs when the number of spatial streams and a receiving channelbandwidth in a reported operating mode are reduced.

FIG. 20 illustrates an example in which disagreement in operating modeoccurs when the number of spatial streams and a receiving channelbandwidth in a reported operating mode are increased.

FIG. 21 illustrates another example of control information used toreport an operating mode.

FIG. 22 illustrates an example in which a reported operating mode isused for the reception operation of a particular STA in an SU mode

FIG. 23 illustrates an example in which a reported operating mode isused for the reception operations of a plurality of STAs in an MU mode.

FIG. 24 is a flowchart illustrating a procedure for processing controlinformation for configuring a PPDU according to an embodiment.

FIG. 25 is a block view illustrating a wireless device to which theexemplary embodiment of the present invention can be applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructurebasic service set (BSS) of institute of electrical and electronicengineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may includeone or more infrastructure BSSs 100 and 105 (hereinafter, referred to asBSS). The BSSs 100 and 105 as a set of an AP and an STA such as anaccess point (AP) 125 and a station (STA1) 100-1 which are successfullysynchronized to communicate with each other are not concepts indicatinga specific region. The BSS 105 may include one or more STAs 105-1 and105-2 which may be joined to one AP 130.

The BSS may include at least one STA, APs providing a distributionservice, and a distribution system (DS) 110 connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 extended by connecting the multiple BSSs 100 and 105. The ESS 140may be used as a term indicating one network configured by connectingone or more APs 125 or 230 through the distribution system 110. The APincluded in one ESS 140 may have the same service set identification(SSID).

A portal 120 may serve as a bridge which connects the wireless LANnetwork (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network betweenthe APs 125 and 130 and a network between the APs 125 and 130 and theSTAs 100-1, 105-1, and 105-2 may be implemented. However, the network isconfigured even between the STAs without the APs 125 and 130 to performcommunication. A network in which the communication is performed byconfiguring the network even between the STAs without the APs 125 and130 is defined as an Ad-Hoc network or an independent basic service set(IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating theIBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operatesin an Ad-Hoc mode. Since the IBSS does not include the access point(AP), a centralized management entity that performs a managementfunction at the center does not exist. That is, in the IBSS, STAs 150-1,150-2, 150-3, 155-4, and 155-5 are managed by a distributed manner. Inthe IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may beconstituted by movable STAs and are not permitted to access the DS toconstitute a self-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

As illustrated in FIG. 2, various types of PHY protocol data units(PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. In detail,LTF and STF fields include a training signal, SIG-A and SIG-B includecontrol information for a receiving STA, and a data field includes userdata corresponding to a PSDU.

In the embodiment, an improved technique is provided, which isassociated with a signal (alternatively, a control information field)used for the data field of the PPDU. The signal provided in theembodiment may be applied onto high efficiency PPDU (HE PPDU) accordingto an IEEE 802.11ax standard. That is, the signal improved in theembodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. TheHE-SIG-A and the HE-SIG-B may be represented even as the SIG-A andSIG-B, respectively. However, the improved signal proposed in theembodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-Bstandard and may be applied to control/data fields having various names,which include the control information in a wireless communication systemtransferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be theHE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is oneexample of the PPDU for multiple users and only the PPDU for themultiple users may include the HE-SIG-B and the corresponding HE SIG-Bmay be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted during an illustrated time period (that is, 4 or 8 μs).

More detailed description of the respective fields of FIG. 3 will bemade below.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding to tone(that is, subcarriers) of different numbers are used to constitute somefields of the HE-PPDU. For example, the resources may be allocated bythe unit of the RU illustrated for the HE-STF, the HE-LTF, and the datafield.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, unitscorresponding to 26 tones). 6 tones may be used as a guard band in aleftmost band of the 20 MHz band and 5 tones may be used as the guardband in a rightmost band of the 20 MHz band. Further, 7 DC tones may beinserted into a center band, that is, a DC band and a 26-unitcorresponding to each 13 tones may be present at left and right sides ofthe DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated toother bands. Each unit may be allocated for a receiving STA, that is, auser.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for asingle user (SU) in addition to the multiple users (MUs) and in thiscase, as illustrated in a lowermost part of FIG. 4, one 242-unit may beused and in this case, three DC tones may be inserted.

In one example of FIG. 4, RUs having various sizes, that is, a 26-RU, a52-RU, a 106-RU, a 242-RU, and the like are proposed, and as a result,since detailed sizes of the RUs may extend or increase, the embodimentis not limited to a detailed size (that is, the number of correspondingtones) of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the likemay be used even in one example of FIG. 5. Further, 5 DC tones may beinserted into a center frequency, 12 tones may be used as the guard bandin the leftmost band of the 40 MHz band and 11 tones may be used as theguard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used forthe single user, the 484-RU may be used. That is, the detailed number ofRUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU,and the like may be used even in one example of FIG. 6. Further, 7 DCtones may be inserted into the center frequency, 12 tones may be used asthe guard band in the leftmost band of the 80 MHz band and 11 tones maybe used as the guard band in the rightmost band of the 80 MHz band. Inaddition, the 26-RU may be used, which uses 13 tones positioned at eachof left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for thesingle user, 996-RU may be used and in this case, 5 DC tones may beinserted. Meanwhile, the detailed number of RUs may be modifiedsimilarly to one example of each of FIG. 4 or 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing theHE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF 700 may include a short training orthogonalfrequency division multiplexing (OFDM) symbol. The L-STF 700 may be usedfor frame detection, automatic gain control (AGC), diversity detection,and coarse frequency/time synchronization.

An L-LTF 710 may include a long training orthogonal frequency divisionmultiplexing (OFDM) symbol. The L-LTF 710 may be used for finefrequency/time synchronization and channel prediction.

An L-SIG 720 may be used for transmitting control information. The L-SIG720 may include information regarding a data rate and a data length.Further, the L-SIG 720 may be repeatedly transmitted. That is, a newformat, in which the L-SIG 720 is repeated (for example, may be referredto as R-LSIG) may be configured.

An HE-SIG-A 730 may include the control information common to thereceiving STA.

In detail, the HE-SIG-A 730 may include information on 1) a DL/ULindicator, 2) a BSS color field indicating an identify of a BSS, 3) afield indicating a remaining time of a current TXOP period, 4) abandwidth field indicating at least one of 20, 40, 80, 160 and 80+80MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6)an indication field regarding whether the HE-SIG-B is modulated by adual subcarrier modulation technique for MCS, 7) a field indicating thenumber of symbols used for the HE-SIG-B, 8) a field indicating whetherthe HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) afield indicating the number of symbols of the HE-LTF, 10) a fieldindicating the length of the HE-LTF and a CP length, 11) a fieldindicating whether an OFDM symbol is present for LDPC coding, 12) afield indicating control information regarding packet extension (PE),13) a field indicating information on a CRC field of the HE-SIG-A, andthe like. A detailed field of the HE-SIG-A may be added or partiallyomitted. Further, some fields of the HE-SIG-A may be partially added oromitted in other environments other than a multi-user (MU) environment

An HE-SIG-B 740 may be included only in the case of the PPDU for themultiple users (MUs) as described above. Principally, an HE-SIG-A 750 oran HE-SIG-B 760 may include resource allocation information(alternatively, virtual resource allocation information) for at leastone receiving STA.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field ata frontmost part and the corresponding common field is separated from afield which follows therebehind to be encoded. That is, as illustratedin FIG. 8, the HE-SIG-B field may include a common field including thecommon control information and a user-specific field includinguser-specific control information. In this case, the common field mayinclude a CRC field corresponding to the common field, and the like andmay be coded to be one BCC block. The user-specific field subsequentthereafter may be coded to be one BCC block including the “user-specificfield” for 2 users and a CRC field corresponding thereto as illustratedin FIG. 8.

A previous field of the HE-SIG-B 740 may be transmitted in a duplicatedform on an MU PPDU. In the case of the HE-SIG-B 740, the HE-SIG-B 740transmitted in some frequency band (e.g., a fourth frequency band) mayeven include control information for a data field corresponding to acorresponding frequency band (that is, the fourth frequency band) and adata field of another frequency band (e.g., a second frequency band)other than the corresponding frequency band. Further, a format may beprovided, in which the HE-SIG-B 740 in a specific frequency band (e.g.,the second frequency band) is duplicated with the HE-SIG-B 740 ofanother frequency band (e.g., the fourth frequency band). Alternatively,the HE-SIG B 740 may be transmitted in an encoded form on alltransmission resources. A field after the HE-SIG B 740 may includeindividual information for respective receiving STAs receiving the PPDU.

The HE-STF 750 may be used for improving automatic gain controlestimation in a multiple input multiple output (MIMO) environment or anOFDMA environment.

The HE-LTF 760 may be used for estimating a channel in the MIMOenvironment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform(IFFT) applied to the HE-STF 750 and the field after the HE-STF 750, andthe size of the FFT/IFFT applied to the field before the HE-STF 750 maybe different from each other. For example, the size of the FFT/IFFTapplied to the HE-STF 750 and the field after the HE-STF 750 may be fourtimes larger than the size of the FFT/IFFT applied to the field beforethe HE-STF 750.

For example, when at least one field of the L-STF 700, the L-LTF 710,the L-SIG 720, the HE-SIG-A 730, and the HE-SIG-B 740 on the PPDU ofFIG. 7 is referred to as a first field, at least one of the data field770, the HE-STF 750, and the HE-LTF 760 may be referred to as a secondfield. The first field may include a field associated with a legacysystem and the second field may include a field associated with an HEsystem. In this case, the fast Fourier transform (FFT) size and theinverse fast Fourier transform (IFFT) size may be defined as a sizewhich is N (N is a natural number, e.g., N=1, 2, and 4) times largerthan the FFT/IFFT size used in the legacy wireless LAN system. That is,the FFT/IFFT having the size may be applied, which is N (=4) timeslarger than the first field of the HE PPDU. For example, 256 FFT/IFFTmay be applied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied toa bandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a sizewhich is 1/N times (N is the natural number, e.g., N=4, the subcarrierspacing is set to 78.125 kHz) the subcarrier space used in the legacywireless LAN system. That is, subcarrier spacing having a size of 312.5kHz, which is legacy subcarrier spacing may be applied to the firstfield of the HE PPDU and a subcarrier space having a size of 78.125 kHzmay be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the firstfield may be expressed to be N (=4) times shorter than the IDFT/DFTperiod applied to each data symbol of the second field. That is, theIDFT/DFT length applied to each symbol of the first field of the HE PPDUmay be expressed as 3.2 μs and the IDFT/DFT length applied to eachsymbol of the second field of the HE PPDU may be expressed as 3.2μs*4(=12.8 μs). The length of the OFDM symbol may be a value acquired byadding the length of a guard interval (GI) to the IDFT/DFT length. Thelength of the GI may have various values such as 0.4 μs, 0.8 μs, 1.6 μs,2.4 μs, and 3.2 μs.

For simplicity in the description, in FIG. 7, it is expressed that afrequency band used by the first field and a frequency band used by thesecond field accurately coincide with each other, but both frequencybands may not completely coincide with each other, in actual. Forexample, a primary band of the first field (L-STF, L-LTF, L-SIG,HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may bethe same as the most portions of a frequency band of the second field(HE-STF, HE-LTF, and Data), but boundary surfaces of the respectivefrequency bands may not coincide with each other. As illustrated inFIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones,and the like are inserted during arranging the RUs, it may be difficultto accurately adjust the boundary surfaces.

The user (e.g., a receiving STA) may receive the HE-SIG-A 730 and may beinstructed to receive the downlink PPDU based on the HE-SIG-A 730. Inthis case, the STA may perform decoding based on the FFT size changedfrom the HE-STF 750 and the field after the HE-STF 750. On the contrary,when the STA may not be instructed to receive the downlink PPDU based onthe HE-SIG-A 730, the STA may stop the decoding and configure a networkallocation vector (NAV). A cyclic prefix (CP) of the HE-STF 750 may havea larger size than the CP of another field and the during the CP period,the STA may perform the decoding for the downlink PPDU by changing theFFT size.

Hereinafter, in the embodiment of the present invention, data(alternatively, or a frame) which the AP transmits to the STA may beexpressed as a terms called downlink data (alternatively, a downlinkframe) and data (alternatively, a frame) which the STA transmits to theAP may be expressed as a term called uplink data (alternatively, anuplink frame). Further, transmission from the AP to the STA may beexpressed as downlink transmission and transmission from the STA to theAP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and datatransmitted through the downlink transmission may be expressed as termssuch as a downlink PPDU, a downlink frame, and downlink data,respectively. The PPDU may be a data unit including a PPDU header and aphysical layer service data unit (PSDU) (alternatively, a MAC protocoldata unit (MPDU)). The PPDU header may include a PHY header and a PHYpreamble and the PSDU (alternatively, MPDU) may include the frame orindicate the frame (alternatively, an information unit of the MAC layer)or be a data unit indicating the frame. The PHY header may be expressedas a physical layer convergence protocol (PLCP) header as another termand the PHY preamble may be expressed as a PLCP preamble as anotherterm.

Further, a PPDU, a frame, and data transmitted through the uplinktransmission may be expressed as terms such as an uplink PPDU, an uplinkframe, and uplink data, respectively.

In the wireless LAN system to which the embodiment of the presentdescription is applied, the whole bandwidth may be used for downlinktransmission to one STA and uplink transmission to one STA. Further, inthe wireless LAN system to which the embodiment of the presentdescription is applied, the AP may perform downlink (DL) multi-user (MU)transmission based on multiple input multiple output (MU MIMO) and thetransmission may be expressed as a term called DL MU MIMO transmission.

In addition, in the wireless LAN system according to the embodiment, anorthogonal frequency division multiple access (OFDMA) based transmissionmethod is preferably supported for the uplink transmission and/ordownlink transmission. That is, data units (e.g., RUs) corresponding todifferent frequency resources are allocated to the user to performuplink/downlink communication. In detail, in the wireless LAN systemaccording to the embodiment, the AP may perform the DL MU transmissionbased on the OFDMA and the transmission may be expressed as a termcalled DL MU OFDMA transmission. When the DL MU OFDMA transmission isperformed, the AP may transmit the downlink data (alternatively, thedownlink frame and the downlink PPDU) to the plurality of respectiveSTAs through the plurality of respective frequency resources on anoverlapped time resource. The plurality of frequency resources may be aplurality of subbands (alternatively, sub channels) or a plurality ofresource units (RUs). The DL MU OFDMA transmission may be used togetherwith the DL MU MIMO transmission. For example, the DL MU MIMOtransmission based on a plurality of space-time streams (alternatively,spatial streams) may be performed on a specific subband (alternatively,sub channel) allocated for the DL MU OFDMA transmission.

Further, in the wireless LAN system according to the embodiment, uplinkmulti-user (UL MU) transmission in which the plurality of STAs transmitsdata to the AP on the same time resource may be supported. Uplinktransmission on the overlapped time resource by the plurality ofrespective STAs may be performed on a frequency domain or a spatialdomain.

When the uplink transmission by the plurality of respective STAs isperformed on the frequency domain, different frequency resources may beallocated to the plurality of respective STAs as uplink transmissionresources based on the OFDMA. The different frequency resources may bedifferent subbands (alternatively, sub channels) or different resourcesunits (RUs). The plurality of respective STAs may transmit uplink datato the AP through different frequency resources. The transmission methodthrough the different frequency resources may be expressed as a termcalled a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs isperformed on the spatial domain, different time-space streams(alternatively, spatial streams) may be allocated to the plurality ofrespective STAs and the plurality of respective STAs may transmit theuplink data to the AP through the different time-space streams. Thetransmission method through the different spatial streams may beexpressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be usedtogether with each other. For example, the UL MU MIMO transmission basedon the plurality of space-time streams (alternatively, spatial streams)may be performed on a specific subband (alternatively, sub channel)allocated for the UL MU OFDMA transmission.

In the legacy wireless LAN system which does not support the MU OFDMAtransmission, a multi-channel allocation method is used for allocating awider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. Whena channel unit is 20 MHz, multiple channels may include a plurality of20 MHz-channels. In the multi-channel allocation method, a primarychannel rule is used to allocate the wider bandwidth to the terminal.When the primary channel rule is used, there is a limit for allocatingthe wider bandwidth to the terminal. In detail, according to the primarychannel rule, when a secondary channel adjacent to a primary channel isused in an overlapped BSS (OBSS) and is thus busy, the STA may useremaining channels other than the primary channel. Therefore, since theSTA may transmit the frame only to the primary channel, the STA receivesa limit for transmission of the frame through the multiple channels.That is, in the legacy wireless LAN system, the primary channel ruleused for allocating the multiple channels may be a large limit inobtaining a high throughput by operating the wider bandwidth in acurrent wireless LAN environment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a wireless LAN systemis disclosed, which supports the OFDMA technology. That is, the OFDMAtechnique may be applied to at least one of downlink and uplink.Further, the MU-MIMO technique may be additionally applied to at leastone of downlink and uplink. When the OFDMA technique is used, themultiple channels may be simultaneously used by not one terminal butmultiple terminals without the limit by the primary channel rule.Therefore, the wider bandwidth may be operated to improve efficiency ofoperating a wireless resource.

As described above, in case the uplink transmission performed by each ofthe multiple STAs (e.g., non-AP STAs) is performed within the frequencydomain, the AP may allocate different frequency resources respective toeach of the multiple STAs as uplink transmission resources based onOFDMA. Additionally, as described above, the frequency resources eachbeing different from one another may correspond to different subbands(or sub-channels) or different resource units (RUs).

The different frequency resources respective to each of the multipleSTAs are indicated through a trigger frame.

FIG. 9 illustrates an example of a trigger frame. The trigger frame ofFIG. 9 allocates resources for Uplink Multiple-User (MU) transmissionand may be transmitted from the AP. The trigger frame may be configuredas a MAC frame and may be included in the PPDU. For example, the triggerframe may be transmitted through the PPDU shown in FIG. 3, through thelegacy PPDU shown in FIG. 2, or through a certain PPDU, which is newlydesigned for the corresponding trigger frame. In case the trigger frameis transmitted through the PPDU of FIG. 3, the trigger frame may beincluded in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or otherfields may be added. Moreover, the length of each field may be varieddifferently as shown in the drawing.

A Frame Control field 910 shown in FIG. 9 may include informationrelated to a version of the MAC protocol and other additional controlinformation, and a Duration field 920 may include time information forconfiguring a NAV or information related to an identifier (e.g., AID) ofthe user equipment.

In addition, the RA field 930 may include address information of thereceiving STA of a corresponding trigger frame, and may be optionallyomitted. The TA field 940 includes address information of an STA (e.g.,AP) for transmitting the trigger frame, and the common information field950 includes common control information applied to the receiving STA forreceiving the trigger frame.

FIG. 10 illustrates an example of a sub-field included in a per userinformation field. Some parts of the sub-field of FIG. 10 may beomitted, and extra sub-fields may be added. Further, a length of each ofthe sub-fields shown herein may change.

As shown in the drawing, the Length field 1010 may be given that samevalue as the Length field of the L-SIG field of the uplink PPDU, whichis transmitted in response to the corresponding trigger frame, and theLength field of the L-SIG field of the uplink PPDU indicates the lengthof the uplink PPDU. As a result, the Length field 1010 of the triggerframe may be used for indicating the length of its respective uplinkPPDU.

Additionally, a Cascade Indicator field 1020 indicates whether or not acascade operation is performed. The cascade operation refers to adownlink MU transmission and an uplink MU transmission being performedsimultaneously within the same TXOP. More specifically, this refers to acase when a downlink MU transmission is first performed, and, then,after a predetermined period of time (e.g., SIFS), an uplink MUtransmission is performed. During the cascade operation, only onetransmitting device performing downlink communication (e.g., AP) mayexist, and multiple transmitting devices performing uplink communication(e.g., non-AP) may exist.

A CS Request field 1030 indicates whether or not the status or NAV of awireless medium is required to be considered in a situation where areceiving device that has received the corresponding trigger frametransmits the respective uplink PPDU.

A HE-SIG-A information field 1040 may include information controllingthe content of a SIG-A field (i.e., HE-SIG-A field) of an uplink PPDU,which is being transmitted in response to the corresponding triggerframe.

A CP and LTF type field 1050 may include information on a LTF length anda CP length of the uplink PPDU being transmitted in response to thecorresponding trigger frame. A trigger type field 1060 may indicate apurpose for which the corresponding trigger frame is being used, e.g.,general triggering, triggering for beamforming, and so on, a request fora Block ACK/NACK, and so on.

Meanwhile, the remaining description on FIG. 9 will be additionallyprovided as described below.

It is preferable that the trigger frame includes per user informationfields 960#1 to 960# N corresponding to the number of receiving STAsreceiving the trigger frame of FIG. 9. The per user information fieldmay also be referred to as a “RU Allocation field”.

Additionally, the trigger frame of FIG. 9 may include a Padding field970 and a Sequence field 980.

It is preferable that each of the per user information fields 960#1 to960# N shown in FIG. 9 further includes multiple sub-fields.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field. Among the sub-fields of FIG. 11, some may beomitted, and other additional sub-fields may also be added.Additionally, the length of each of the sub-fields shown in the drawingmay be varied.

A User Identifier field 1110 indicates an identifier of an STA (i.e.,receiving STA) to which the per user information corresponds, and anexample of the identifier may correspond to all or part of the AID.

Additionally, a RU Allocation field 1120 may be included in thesub-field of the per user information field. More specifically, in casea receiving STA, which is identified by the User Identifier field 1110,transmits an uplink PPDU in response to the trigger frame of FIG. 9, thecorresponding uplink PPDU is transmitted through the RU, which isindicated by the RU Allocation field 1120. In this case, it ispreferable that the RU that is being indicated by the RU Allocationfield 1120 corresponds to the RU shown in FIG. 4, FIG. 5, and FIG. 6.

The sub-field of FIG. 11 may include a Coding Type field 1130. TheCoding Type field 1130 may indicate a coding type of the uplink PPDUbeing transmitted in response to the trigger frame of FIG. 9. Forexample, in case BBC coding is applied to the uplink PPDU, the CodingType field 1130 may be set to ‘1’, and, in case LDPC coding is appliedto the uplink PPDU, the Coding Type field 1130 may be set to ‘0’.

Additionally, the sub-field of FIG. 11 may include a MCS field 1140. TheMCS field 1140 may indicate a MCS scheme being applied to the uplinkPPDU that is transmitted in response to the trigger frame of FIG. 9.

Hereinafter, the exemplary embodiment of the present invention relatesto an operating mode that is used in an STA (e.g., AP and/or non-AP STA)of a wireless LAN system.

The operating mode may be categorized as a transmit operating mode and areceive operating mode. The receive operating mode relates to operationsof a STA (e.g., non-AP STA) that has reported its operating modereceiving a signal from its opposite STA (e.g., AP). Conversely, thetransmit operating mode relates to operations of the opposite STA (e.g.,AP) transmitting a signal to the STA (e.g., non-AP STA) that hasreported its operating mode. For example, the transmit operating modemay be used for the UL MU PPDU, which is simultaneously transmitted bymultiple STAs in response to the trigger frame of FIG. 9.

FIG. 12 illustrates an example of control information 1200 used toreport an operating mode.

As shown in the drawing, the control information 1200 may include all orpart of multiple subfields 1210, 1220, 1230, and 1240, and the controlinformation 1200 may also additionally include subfields that are notshown in the drawing. The control information 1200 of FIG. 12 may beincluded in a MAC frame, which is included in a data field of the PPDU.

A Rx NSS subfield 1210 of FIG. 12 may indicate a maximum number ofspatial streams that are used when the STA (e.g., non-AP STA), whichreports the control information 1200, receives a signal/PPDU. Forexample, the Rx NSS subfield 1210 may be configured of an informationfield by using 3 bits.

For example, the Rx NSS subfield 1210 of FIG. 12 may indicate the numberof spatial streams that are used when the STA receives a downlink PPDU.More specifically, when the AP configures a PPDU for a specificreceiving STA, the AP may refer to the corresponding subfield 1210.

A Channel Width subfield 1220 of FIG. 12 may indicate an operatingchannel that is supported by the STA (e.g., non-AP STA), which reportsthe control information 1200. More specifically, this may indicate amaximum level (or size) of the operating channel supported by the STA,for example, the value of “0” may indicate 20 MHz, the value of “1” mayindicate 40 MHz, the value of “2” may indicate 80 MHz, and the value of“3” may indicate 160 MHz or 80+80 MHz. The Channel Width subfield 1220may commonly indicate a transmitting channel and a receiving channelthat are used by the STA, which reports the control information 1200.

A UL MU Disable subfield 1230 of FIG. 12 may indicate whether or not theSTA (e.g., non-AP STA), which reports the control information 1200,supports UL MU operations. For example, in case an UL MU operation issuspended due to a particular reason, a specific value (e.g., “1”) maybe indicated, and, in case the UL MU operation is resumed, another value(e.g., “0”) may be indicated.

The UL MU Disable subfield 1230 may be used in a UL MU operation that isassociated with the trigger frame of FIG. 9. In order to perform anadequate UL MU communication, the AP may verify whether or not UL MU issupported by a specific non-AP STA. More specifically, when configuringa trigger frame (i.e., the trigger frame shown in FIG. 9) for the UL MUcommunication, the corresponding subfield 1230 may be used.

A Tx NSS subfield 1240 of FIG. 12 may indicate a maximum number ofspatial streams that are used when the STA (e.g., non-AP STA), whichreports the control information 1200, transmits a signal/PPDU.

Although the example shown in FIG. 12 corresponds to an example, whereinthe Rx NSS 1210 and the Tx NSS 1240 are configured as separatesubfields, the corresponding subfields may be modified (or changed). Forexample, it is possible to commonly indicate the Rx NSS (i.e., a numberof spatial streams being used in a specific STA for PPDU reception) andthe Tx NSS (i.e., a number of spatial streams being used in a specificSTA for PPDU transmission) through a single NSS subfield.

FIG. 13 illustrates an example of the reported operating mode being usedfor UL MU operations.

The example shown in FIG. 13 corresponds to operations between a firstSTA and a second STA, wherein the first STA may correspond to the AP1301 and the second STA may correspond to the STA 1302. In the exampleshown in FIG. 13, STA1 1302 corresponds to a STA that reports theoperating mode to the AP 1301. STA1 1302 may transmit a PPDU including adata field 1310 to the AP 1301 during a first TXOP 1305, and thecorresponding data field 1310 may include the control information 1200of FIG. 12. The AP 1301 may transmit a block ACK (BA) 1320 indicatingthat the corresponding data field 1310 has been successfully received tothe AP 1301.

The AP 1301 may be informed of the transmit operating mode and thereceive operating mode of STA1 1302 through the corresponding data field1310, and, afterwards, in case UL MU communication is performed from theAP 1301 through a trigger frame 1330, information on the transmitoperating mode may be used. More specifically, the AP 1301, whichintends to receive an uplink PPDU from multiple STAs including STA11302, may ensure a TXOP 1325 via contending, and so on, and then the AP1301 may transmit a trigger frame 1330 to the multiple STAs. An exampleof the trigger frame may be configured in accordance with the exampleshown in FIG. 9 to FIG. 11. More specifically, the AP 1301 may beconfigured to transmit an uplink PPDU 1341 to STA1 1302 through thetrigger frame 1330 by using a specific RU, and, herein, in case abandwidth (i.e., RU) for the uplink PPDU 1341 is allocated, the ChannelWidth subfield 1220, which is indicated in the data field 1310, may beused. Additionally, the AP 1301 may indicate a number of spatial streamsthat may be used for the uplink PPDU 1341 to STA1 1302 through thetrigger frame 1330. In this case, the number of spatial streams that areused by STA1 1302 for the uplink PPDU 1341 may be signaled through asubfield, which is newly configured in the per user information field ofFIG. 11.

In summary, when the AP 1301 transmits the trigger frame 1330, uplinkPPDUs 1341 and 1342 are received from multiple STAs through acommunication method and a radio resource that are indicated by thetrigger frame 1330. Herein, the communication method and radio resourcethat are indicated by the trigger frame 1330 may be determined based onthe information related to the operating mode, which has already beenreported to the AP 1301. More specifically, it is preferable that thenumber of spatial streams for STA1 1302 indicated in the trigger frame1330 is determined to be equal to or smaller than a value of the Tx NSSsubfield 1240, which is indicated by the control information 1200 beingcarried through the data field 1310. Additionally, it is preferable thefrequency band (i.e., RU) for STA1 1302 that is indicated by the triggerframe 1330 is determined to be equal to or smaller than a value of theChannel Width subfield 1220, which is indicated by the controlinformation 1200 being carried through the data field 1310.

Meanwhile, it may be possible that STA1 1302 does not participate in theUL MU communication for diverse reasons. In this case, by setting the ULMU Disable subfield 1230 of the control information 1200, which iscarried through the data field 1310, to a specific value (e.g., “1”),this may allow the AP 1301 to notify that STA1 1302 cannot participatein the UL MU communication. In case the UL MU Disable subfield 1230corresponding to STA1 1302 is set to the specific value, the AP 1301 maynot allocate uplink PPDUs 1341 and 1342 corresponding to the triggerframe for the corresponding STA1 1302.

FIG. 14 illustrates an example of the reported operating mode being usedfor receiving operations of a specific STA.

In case the operating mode shown in FIG. 12 is reported, i.e., in casethe second STA 1402 reports the operating mode to the first STA 1410, itis preferable that the application time of the reported operating modeis indicted clearly. The example of FIG. 14 corresponds to an examplerelates to a case when the second STA 1402 corresponds to a Non-AP STAand the first STA 1401 corresponds to an AP.

In the example of FIG. 14, in case the operating mode shown in FIG. 12is reported through the data field 1410, the AP 1401 may already havedownlink data stored in its queue. The downlink data that are already instorage are not required to be transmitted to the PPDU according to theoperating mode (i.e., “new operating mode”), which was reported throughthe data field 1410. In other words, transmitting the downlink data thatare already in storage to the PPDU according to the “previous (or old)operating mode” may be helpful in decreasing latency and enhancing MUthroughput.

Accordingly, the example of FIG. 14 proposes a method of indicatingwhether or not to delay the application of the operating mode (i.e., newoperating mode) that was reported by the AP 1401. More specifically,when the STA 1402 reports the new operating mode through the data field1410, the AP 1401 transmits a block ACK 1420 in response to thecorresponding data field 1410. Information on whether or not theapplication of the new operating mode is being delayed is indicated inthe corresponding BA 1420. More specifically, in case the “delayrequired” is indicated by a specific value (i.e., “1”), the AP 1401 maytransmit a PPDU to the STA 1402 by using the previous (or old) operatingmode instead of the new operating mode during a predetermined delay time1410. Meanwhile, after the delay time 1410, a transition time 1420 mayexist. During the transition time 1420, the AP 1401 may shift itsoperating mode from the previous (or old) operating mode to the newoperating mode. After an elapse of the transition time 1420, the AP 1401may transmit a PPDU to the STA 1402 in accordance with the new operatingmode that is reported through the data field 1410.

The delay time and/or transition time of FIG. 14 may be negotiatedthrough a management frame, and an example of such management frame mayinclude an association request/response. Since such delay time and/ortransition time are/is not required to exist, the length of thecorresponding time(s) may be set to “0”. Additionally, the delay timeand/or transition time may be negotiated through a MAC header (e.g., HEcontrol field, etc.), which is included in the data field 1410. Forexample, the STA 1402 may set the length of the delay time and/ortransition time to “0” in the data field 1410, and, in this case, the AP1401 may apply the operating mode without the delay time and/ortransition time.

FIG. 15 illustrates an additional example of the reported operating modebeing used for the receiving operations of a specific STA. The exampleof FIG. 15, which is similar to the example shown in FIG. 14,corresponds to an example of delaying the application of a new operatingmode. The example of FIG. 15 corresponds to an example of not applyingthe new operating mode during an implicitly indicated time period (ortime interval), e.g., during a transmission opportunity (TXOP). The termTXOP is a term, which is well-known to anyone skilled in fields relevantto wireless LAN systems, and which is defined as an interval of timeduring which a particular STA has the right to initiate frame exchangesequences onto the wireless medium.

The example of FIG. 15 may be applied to different STAs. For example,FIG. 15 shows an example in which a first STA 1501 corresponds to an APSTA and a second STA 1502 corresponds to a non-AP STA.

More specifically, the AP 1501 or STA 1502 may ensure a first TXOP 1550via contending, and, afterwards, the STA 1502 may report a new operatingmode to the AP 1501 while transmitting a PPDU including a data field1510 to the AP 1501. For example, the Rx NSS subfield 1210 may indicate2 (two) receiving spatial streams (RX NSS=2) through the controlinformation 1200, which is included in the data field 1510, and aChannel Width subfield 1220 may indicate a bandwidth of 40 MHz.Thereafter, the AP 1501 transmits a Block ACK 1520 in response to thecorresponding data field 1510.

Since the example shown in FIG. 15 corresponds to an example of notapplying the new operating mode during an implicitly indicated timeinterval (or time period), additional signaling related to the delaytime is not required in the Block ACK 1520. In case a PPDU 1530 for theSTA 1502 is configured during the first TXOP 1550, the AP 1501 delaysthe application of the received control information 1200 so that the newoperating mode is not applied during the first TXOP 1550. Accordingly,instead of having the newly received control information 1200 appliedthereto, the operating mode that has been applied since earlier isapplied to the PPDU 1530, which is configured in the first TXOP 1550period (or interval). If the PPDU 1530 is successfully received, the STA1502 may transmit a Block ACK 1540.

After the termination of the first TXOP 1550, during which indicationinformation (i.e., a subfield of the control information 1200 beingincluded in the data field 1510) indicating the change in the operatingmode is carried (or delivered) to the AP 1501, the indicationinformation (i.e., a subfield of the control information 1200 beingincluded in the data field 1510) that has already been carried (ordelivered) is applied. Similarly to the example shown in FIG. 14,although a transition time 1560 for the AP 1501 may be applied,immediately after the first TXOP 1550, such transition time 1560 is notrequired and may be omitted. During the corresponding transition time1560, the AP 1501 may not transmit any PPDUs in order to apply the newoperating mode.

After the termination of the above-described first TXOP 1550, a newsecond TXOP 1570 may be acquired by the AP 1501/STA 1502. Since a timeperiod (or interval), during which the application of the new operatingmode is delayed, is limited to the first TXOP 1550, a PPDU that isconfigured by the AP 1501 during the second TXOP 1570 is configuredbased on the new operating mode, even if there is no separate signaling.In the example of FIG. 15, since the Rx NSS subfield 1210 indicates 2(two) receiving spatial streams (RX NSS=2) through the controlinformation 1200 that is included in the data field 1510, and since theChannel Width subfield 1220 indicates a bandwidth of 40 MHz, a new PPDU1580 is configured based on such indications. The STA 1502 receives thenewly configured PPDU 1580 and transmits a Block ACK 1590 in response tothe received PPDU 1580.

A mechanism for indicating an operating mode in the presentspecification is illustrated below.

First, an ROM indication method is described. In the suggested method,STA 2, which has received ROM indication information from STA 1, reportsusing reserved bits of a BA/ACK (or multi-TID BA, OFDMA-BA, or the like)whether to accept or deny an ROM. According to the method suggested inthe present specification, STA 2 indicates an appropriate ROM for STA 1.

For example, reserved bits (8 bits) in a BA Control field may be used asfollows.

1 bit: Indicator indicating whether STA 2 accepts or denies an ROMrequested by STA 1

1 bit: Indicator indicating whether STA 2 transmits an appropriate ROMfor STA 1 (applied similar to an ROM request bit)

3 bits: The number of receiving spatial streams

3 bits: A receiving channel bandwidth

If STA 2 accepts the ROM, STA 2 may omit transmitting relevantinformation, such as an indicator indicating whether STA 2 transmits anappropriate ROM for STA 1, the number of receiving spatial streams, anda receiving channel bandwidth. Further, if STA 2 accepts the ROM, STA 2may retransmit the ROM information for confirmation.

Alternatively, STA 2 may report the foregoing information further usingreserved values among Multi-TID, Compressed Bitmap, and GCR bits.

Alternatively, STA 2 may transmit a BA frame using reserved bits,thereby reporting whether to accept or deny the ROM received from STA 1.Further, STA 2 may transmit a BA frame to report whether to transmit anappropriate ROM for STA 1. Here, STA 2 may transmit appropriate ROMinformation using a BA Information field. That is, STA 2 may transmitinformation on the number of receiving spatial streams or a receivingchannel bandwidth.

Alternatively, STA 2, which has received the ROM from STA 1, may reportwhether to accept or deny the ROM and whether to transmit an appropriateROM using a multi-TID BA (M-BA) frame.

For example, a TID value of the BA Information field is predefined as aspecific value (for example, 0 or 1). When the TID value is set to thespecific value, a Block ACK Starting Sequence Control field and/or BlockACK Bitmap field as subfields of the BA Information field may beomitted. Alternatively, a field transmitted following the TID Valuefield may be defined as a new field indicating the ROM.

Although the foregoing method has been described as indicating whetherSTA 2 accepts or denies the ROM requested by STA 1 and whether STA 2transmits an appropriate ROM, the present invention is not limitedthereto.

STA 2 may transmit ROM information for STA 1 through an MAC Header of aframe (for example, a data frame, a BA/ACK frame, or the like)transmitted by STA 2 or via piggyback. The ROM information may bechannel information and the number of spatial streams for STA 2 totransmit a trigger frame for STA 1 to be subjected to UL MU.

For example, when STA 2 applies UL MU for STA 1, STA 2 may transmitbandwidth or channel information and information on the number ofspatial streams through a BA/ACK (or M-BA, OFDMA-BA, or the like) as aresponse frame to a UL data frame transmitted by STA 1. Alternatively,STA 2 may transmit bandwidth or channel information and information onthe number of spatial streams through a frame (for example, a dataframe) transmitted from STA2 to STA 1. The bandwidth or channelinformation may correspond to information used for STA 2 to transmit anext trigger frame for STA 1. When such information is received, STA 1may perform a subsequent receiving operation according to an ROMindicated by STA 2.

Next, a TOM indication method is described. That is, a method describedin the present specification is not limited to the foregoing ROMchanging operation but may also be applied to a TOM changing operation.

An 802.11ax system allows an STA to arbitrarily perform UL access to aspecific resource for converge extension in view of an outdoorenvironment. Here, it is needed to change a TOM in which the STAperforms transmission. For example, some STAs performing random accessmay access an AP using only 26 tones. When the STA receives a triggerframe (for random access) and transmits a UL frame, the STA may transmitinformation on a TOM of the STA (for example, the maximum RU size, achannel bandwidth, or the number of spatial streams for access to theAP) using reserved bits or a newly defined method. The reserved bits maycorrespond to reserved bits in a newly defined field or frame (ACK/BA,data buffer status report, or the like) of the MAC Header.

Further, an indicator bit indicating an ROM/TOM may be added to indicatean ROM and a TOM using the same format. For example, it may bepredefined that the indicator bit set to 1 indicates a TOM and theindicator bit set to 0 indicates an ROM. When the TOM information isreceived from the STA, the AP may accept or deny whether to change theTOM of the STA. When the AP schedules UL MU transmission of the STAusing the TOM information, the AP may transmit a trigger frame for theUL MU transmission of the STA considering the TOM information. Here, theAP may allocate an RU unit with a size equal to or smaller than themaximum RU size for access to the AP, which is transmitted by the STA,as an RU unit of a UL MU resource for the STA. Alternatively, the AP mayallocate UL MU resources to transmit a smaller number of spatial streamsthan the number of spatial streams which is transmitted by the STA.

When the STA reports that the maximum RU size for the STA to access theAP is 52 tones, the AP may allocate 52 tones or 26 tones when allocatingUL MU resources for the STA.

Next, a method of transmitting a preferred RU size and a preferred MCSvia a buffer status report and transmitting a TXOP length calculatedbased on the RU size and the MCS is described.

When the STA performs a buffer status report upon receiving a triggerframe (for random access), the STA may report to the AP an RU sizepreferred by the STA (or the maximum RU size for access to the AP) andan MCS preferred by the STA (which may be omitted if being the same asan MCS used to transmit a buffer status report, or the maximum MCS levelavailable for the STA). In addition, the STA may transmit a TXOP lengthdetermined based on the RU size and the MCS level preferred by the STA,thereby reporting the amount of buffered data of the STA to the AP.

Next, a backoff procedure is described.

After transmitting the ROM information (when the STA transmits ROMinformation on the STA or requests ROM information on an STA linked tothe STA), the STA receives a response frame (ACK/BA, M-BA, OFDMA BA,data, or the like) to the ROM information. Here, data is included whenaccepting the ROM or receiving information on an appropriate operatingmode. In this case, the STA may change the ROM after a predefined outagetime, and accordingly the transmitting STA may transmit a frame (forexample, a data frame) in view of the changed ROM of the STA linked tothe transmitting STA.

Here, the transmitting STA defers a backoff procedure during the outagetime and performs the backoff procedure after the outage time.

Next, a method for the AP to manage conditions for triggering theROM/TOM report of the STA is described.

The AP (or STA) may manage conditions for triggering the report ofTOM/ROM information by the STA so that the STA transmits TOM/ROMinformation thereof.

For example, in order that the STA is triggered to transmit ROMinformation when a battery is a specific threshold or less, the AP maytransmit the specific threshold using a beacon, a trigger frame, amanagement frame, or the like.

Alternatively, the AP may report using a beacon, a trigger frame, amanagement frame, or the like that the STA is allowed to transmit ROMinformation only when the STA turns off an RF chain (for example, thebandwidth is changed from 160 MHz to 80 MHz).

Further, the AP may report using a beacon, a trigger frame, a managementframe, or the like that the STA is allowed to transmit TOM/ROMinformation only in a specific interval when a beacon interval isdivided into an OFDMA interval and an EDCA interval or into a legacyinterval and an 11ax interval.

For another example, in order that the STA is triggered to transmit TOMinformation when the RSSI (or SNR, SNIR, or the like) of a signal fromthe AP is a specific threshold or less, the AP may transmit the specificthreshold using a beacon, a trigger frame, a management frame, or thelike.

Next, a method of reporting ROM change time is described.

When an AP has DL data for an STA requesting an ROM change, the AP maytransmit the DL data to the STA according to the previous ROM of the STAin order to improve the throughput of the DL data. In particular, whenthe DL data for the STA is MU-transmitted, the AP may perform the aboveoperation to obtain an MU gain.

The AP may defer ROM change time transmitted from the STA for aspecified time using a DL frame (for example, a BA/ACK/M-BA/OFDMA BA ordata frame).

The AP reports the specified time using various methods.

First, the AP may directly report an outage time value. The AP maydirectly transmit the outage time value to the STA along withinformation indicating the acceptance of the ROM change request. Here,the outage time value may be transmitted through an MAC header, using areserved bit of a BA/ACK/M-BA/OFDMA BA, or reusing a specified field ina similar manner to that mentioned above. Alternatively, the outage timevalue may be transmitted through a field newly defined for the STAsupporting an HE system.

Further, the outage time may be predefined. The AP may report using a DLframe (for example, BA/ACK/M-BA/OFDMA BA or data frame) whether the STAapplies the outage time and changes the ROM after the outage time, orchanges the ROM upon receiving a frame including the informationindicating the acceptance of the ROM change request. The followingvalues may be defined as the outage time.

Duration of current TXOP period

Duration of remaining TXOP period (in this case, the STA may change theROM in the next TXOP)

Duration of Max TXOP period

Service Period

Remaining time to next beacon target transmission time (that is, the STAmay change the ROM in the next beacon interval)

Remaining time to later beacon target transmission time (the AP mayindicate which beacon interval)

Next, a method of indicating an ROM change in the 11ax system isdescribed.

An STA may transmit ROM information via an MAC header of a controlframe, a data frame or a management frame, or a PSDU in order to changean ROM thereof. Here, the ROM information reported by the STA mayinclude channel bandwidth information, tone information, RU information,or the number of receiving streams. Further, the STA may further definean RX mode Request bit in order to indicate that the ROM information isfor requesting an ROM change.

When the STA includes the MAC header reporting this information, the STAmay report using a reserved bit in an HT variant field or VHT variantfield of a HT control of the MAC header that a field transmitting theROM information is transmitted through the MAC header.

Here, when STA 1 transmits the ROM information, STA 2 receiving thisinformation may report using a BA/ACK (or an M-BA or OFDMA-BA) whetherto accept or reject the information. Specifically, STA 2 may use areserved bit of a BA/ACK (or an M-BA or OFDMA-BA).

Alternatively, STA 2 may transmit an RX mode Request bit set to 1 inorder to change the ROM of STA 1. STA 1 receiving the RX mode Requestbit may report using a BA/ACK (or an M-BA or OFDMA-BA) whether to acceptor reject the ROM requested by STA 2. Specifically, STA 1 may use areserved bit of a BA/ACK (or an M-BA or OFDMA-BA).

FIG. 16 illustrates an example of a BA frame for a plurality of STAs.For an operating process, the AP transmits a BA in response to datatransmitted from an STA. The BA may indicate using reserved bits of theBA whether there is buffered data in order to indirectly respond to anROM request from the STA. Here, the reserved bits correspond to a morebit of an MAC Header in the data, wherein a more bit (1 bit) is added tothe BA.

The BA frame in FIG. 16 may correspond to an M-BA supported in the802.11ax system. Referring to FIG. 16, the BA frame 1600 includes aplurality of subfields including a BA Control field 1610 and a BAInformation field 1620. The BA Control field 1610 is a common controlfield and the BA Information field 1620 is a user-specific field. Thatis, the BA Information field 1620 may be transferred to each differentSTA. The more bit corresponds to 1 bit among reserved bits 1630 (B4 toB11) in the BA Control field 1610.

That is, the AP may indicate that there is remaining data to transmit toa specific STA using 1 bit among the reserved bits 1630 included in theBA frame 1600, like a more bit of a data MAC header. 1 bit of thereserved bits 1630 may be referred to as the more bit, a more data bit,or a delay required bit.

FIG. 17 illustrates an example of an Aggregated-Control (A-Control)field used to transfer control information.

An STA requests an ROM from an AP to save power. The ROM request may betransmitted through a QoS Null frame or A-Control field. Further, theROM request may also be transmitted through a QoS Data frame, which willbe described.

The A-Control field is illustrated in FIG. 17. The A-Control field 1710is a subfield of an MAC Header (for example, an HE control field), whichis a control field further added following a QoS Control field in the802.11ax system. The A-Control field 1710 includes at least one sequenceof Control subfields (1720-1, 1720-2, . . . , and 1720-N). A Controlsubfield 1720-1 with a Control ID subfield 1730 equal to 0 is a firstsubfield of the sequence.

The Control ID subfield 1730 indicates the type of informationtransferred in a Control Information subfield 1740. The ControlInformation subfield 1740 has a fixed length for each value of theControl ID subfield 1730 that is not deferred. The value of the ControlID subfield 1730 and the length of the Control Information subfield 1740related to the value of the Control ID subfield 1730 are defined as inthe following table.

TABLE 1 Control Length of the Control ID value Meaning Informationsubfield (bits) 0 UL MU response scheduling 26 1 Operating Mode 12 2 HElink adaptation 16 3 Buffer Status Report (BSR) 26 4 UL Power Headroom 85 Bandwidth Query Report (BQR) 10 6-15 Reserved

Referring to Table 1, when the Control ID subfield 1730 is equal to 1,the Control Information subfield 1740 includes information related to anoperating mode change of an STA transmitting a frame includinginformation on an operating mode indication. That is, the format of theControl Information subfield 1740 in the case where the Control IDsubfield 1730 is equal to 1 is illustrated in FIG. 12.

This specification proposes a method for solving the problem of ROMsignaling failure. Specifically, an STA transmits an ROM request tochange Rx values (i.e., Rx NSS and Rx BW), and an AP transmits an ACK/BAin response to the ROM request. However, when the AP transmits theACK/BA but the STA fails to receive the ACK/BA, the STA cannot change anROM.

FIG. 18 illustrates an example in which disagreement in operating modeoccurs between an AP and an STA.

In FIG. 18, it is assumed that the STA has requested an ROM change(1810) but has not received an ACK/BA 1820 of the ROM change from theAP. The STA has not received the ACK/BA 1820 from the AP because acollision has occurred during the transmission of the ACK/BA 1820.

Referring to FIG. 18, since the STA has not received the ACK/BA 1820 ofan ROW, the STA cannot change an ROM. However, the AP may change the ROMas requested by the STA after transmitting the ACK/BA 1820 of the ROMI.That is, the STA applies Rx values before the change and the AP appliesnew Rx values after the change, and thus disagreement in operating modeoccurs between the AP and the STA.

Hereinafter, a method for performing an ROM change to solve the abovedisagreement in operating mode will be described with reference to twoembodiments. Embodiment 1 illustrates a case of reducing Rx NSS and RxBW through an ROM request, and Embodiment 2 illustrates a case ofincreasing Rx NSS and Rx BW through an ROM request.

Embodiment 1: Case of Reducing Rx NSS and Rx B Through ROM Request

FIG. 19 illustrates an example in which disagreement in operating modeoccurs when the number of spatial streams and a receiving channelbandwidth in a reported operating mode are reduced.

FIG. 19 illustrates a procedure in which an STA receives DL data afterthe occurrence of disagreement in operating mode described in FIG. 18.That is, the STA requests an ROM change 1910 but does not receive anACK/BA 1920 of the ROM change from an AP due to the occurrence of acollision during transmission by the AP. Rx NSS and Rx BW values in anROM may be represented by (Rx NSS, Rx BW). The STA has (4, 80) in theROM before the ROM change, but the STA intends to reduce the values inthe ROM to (2, 20) through the ROM request.

Referring to FIG. 19, the STA has not received the ACK/BA 1920 of theROMI and thus cannot change the ROM. However, the AP may change the ROMas requested by the STA after transmitting the ACK/BA 1920 of the ROME.That is, the STA applies Rx values before the change and the AP appliesnew Rx values after the change, and thus disagreement in operating modeoccurs between the AP and the STA.

In this case, even though the AP transmits DL data 1930 by applying thenew Rx values, the STA cannot receive the DL data 1930, because the newRx values applied by the AP are smaller than the Rx values before thechange for the STA. That is, since the AP transmits the DL data 1930 byapplying the values smaller than the number of spatial streams (Rx NSS)and a receiving bandwidth (Rx BW) which are currently supported by theSTA, the STA cannot receive the DL data 1930 via the number of spatialstreams (Rx NSS) and the receiving bandwidth (Rx BW) which are currentlysupported. Therefore, the STA may transmit a BA 1940 of the DL data.

Embodiment 2: Case of Increasing Rx NSS and Rx BW Through ROM Request

FIG. 20 illustrates an example in which disagreement in operating modeoccurs when the number of spatial streams and a receiving channelbandwidth in a reported operating mode are increased.

FIG. 20 illustrates a procedure in which an STA receives DL data afterthe occurrence of disagreement in operating mode described in FIG. 18.That is, the STA requests an ROM change 2010 but does not receive anACK/BA 2020 of the ROM change from an AP due to the occurrence of acollision during transmission by the AP. Rx NSS and Rx BW values in anROM may be represented by (Rx NSS, Rx BW). The STA has (2, 20) in theROM before the ROM change, but the STA intends to increase the values inthe ROM to (4, 80) through the ROM request.

Referring to FIG. 20, the STA has not received the ACK/BA 2020 of theROMI and thus cannot change the ROM. However, the AP may change the ROMas requested by the STA after transmitting the ACK/BA 2020 of the ROMI.That is, the STA applies Rx values before the change and the AP appliesnew Rx values after the change, and thus disagreement in operating modeoccurs between the AP and the STA.

In this case, even though the AP transmits DL data 2030 by applying thenew Rx values, the STA cannot receive the DL data 2030, because the newRx values applied by the AP are greater than the Rx values before thechange for the STA. That is, since the AP transmits the DL data 2030 byapplying the values greater than the number of spatial streams (Rx NSS)and a receiving bandwidth (Rx BW) which are currently supported by theSTA, the STA cannot receive the DL data 2030 via the number of spatialstreams (Rx NSS) and the receiving bandwidth (Rx BW) which are currentlysupported. This is because the new Rx values exceed maximum capacitiesof the number of spatial streams and the receiving bandwidth which theSTA can support.

This specification discloses a method of setting time to apply an ROMchange to solve disagreement in operating mode due to an ROM changerequest, Specifically, the present specification explains whether an APapplies an ROM change after a TXOP interval or immediately applies theROM change upon receiving an ACK of the ROM request when an STA requeststhe ROM change during the TXOP interval.

FIG. 21 illustrates another example of control information used toreport an operating mode.

FIG. 21 shows another embodiment of an ROMI field for requesting an ROM.Referring to FIG. 21, an ROM change indicator bit 2110 may be added tothe ROMI field to explicitly indicate an interval in which an ROM changeis applied. It is assumed that the ROM change indicator bit 2110 is twobits. When the ROM change indicator bit is 00, the ROM change is appliedwithin a TXOP interval. When the ROM change indicator bit is 01, the ROMchange is applied during the next or subsequent TXOP interval after theTXOP interval expires. When the ROM change indicator bit is 10, the ROMchange is immediately applied for a PPDU subsequently transmitted afterreceiving an ACK for an ROM request. When the ROM charge indicator bitis 11, the ROM change indicator bit is left as reserved bits.

Hereinafter, three embodiments of setting time an AP applies an ROMchange will be described.

First, time to apply an ROM change may vary depending on whethercommunication between an AP and an STA is a UL MU mode or a UL SU mode.In the UL MU mode, the AP applies the ROM change after the current TXOPinterval expires. Here, the AP does not immediately apply the ROM changeeven though outage delay present=0. That is, in the current TXOPinterval, after the STA transmits an ROM request, the AP only transmitsan ACK of the ROM request and does not immediately apply the ROM change.The AP applies a changed ROM in the next TXOP interval. In the UL SUmode, the AP immediately applies a changed ROM for a PPDU subsequentlytransmitted after transmitting an ACK of an ROM request transmitted bythe STA. FIGS. 22 and 23 show a TXOP interval in which an ROM change isapplied in the UL SU mode and in the UL MU mode,

FIG. 22 illustrates an example in which a reported operating mode isused for the reception operation of a particular STA in the SU mode.

Referring to FIG. 22, an STA transmits an ROM request 2210 to change anRx value. The ROM request 2210 may be transmitted via a data frame or aQoS null frame. An AP receives the ROM request 2210. The AP transmits aBA 2220 in response to the ROM request.

Here, when outage delay present=1, the AP transmits the BA 2220 andapplies a changed ROM (2, 40) according to the ROM request after theoutage delay. Therefore, the AP transmits DL data 2230 by applying thechanged ROM. When outage delay present=0, the AP transmits the BA 2220and immediately applies the changed ROM (2, 40) according to the ROMrequest.

FIG. 23 illustrates an example in which a reported operating mode isused for the reception operations of a plurality of STAs in the MU mode.

Referring to FIG. 23, an AP transmits a trigger frame 2310. STAs 1 and 2transmit an ROM request 2320 along with a data frame in order to changean Rx value to a resource unit (RU) allocated via the trigger frame. STA3 transmits only an ROM request. STA 4 transmits only a data frame. TheROM requests transmitted by STAs 1, 2, and 3 may be transmitted via adata frame or a QoS null frame.

The AP receives the ROM requests 2320 from the respective STAs. The APmay transmit DL data or an ACK 2330 in response to the ROM requests fromthe respective STAs. This operation may be referred to as a three-wayhandshake scheme.

In the UL MU mode, the AP applies an ROM change during a next TXOPinterval 2350 after a current TXOP interval 2340 expires. Here, whenoutage delay present=1, the AP transmits the DL data or ACK 2330 andapplies a changed ROM according to the ROM request after the outagedelay. Accordingly, the AP can transmit DL data by applying the changedROM during the next TXOP interval 2350. When outage delay present=0, theAP transmits the DL data or ACK 2330 and can immediately apply thechanged ROM according to the ROM request.

In the UL MU mode, the following problems may arise. When outage delaypresent=0 and the AP is a TXOP holder, the AP may determine a TXOPconsidering the amount of packets to be transmitted to each STA, the MCSof the STAs, and an operating bandwidth. Here, when the ROM of aparticular STA is changed (e.g., when Rx BW and Rx NSS are reduced),there may be a problem about scheduling in the current TXOP.

Further, when outage delay present=1, the AP may also determine a TXOPconsidering the amount of packets to be transmitted to each STA, the MCSof the STAs, and an operating bandwidth. Here, when a particular STAchanges an Rx value to cause an outage delay, scheduling for theparticular STA may be impossible within the TXOP or it may be necessaryto set a separate TXOP for the particular STA.

Thus, when an ROM change is requested in the UL MU mode, a changed ROMneeds to be applied from the next TXOP interval, not in the current TXOPinterval.

In another example, time to apply an ROM change may vary depending onwhether an outage delay is present (outage delay present=1) or an outagedelay absent (outage delay present=0). For example, when outage delaypresent=0, the AP immediately applies a changed ROM for a PPDUsubsequently transmitted after transmitting an ACK of an ROM requesttransmitted by the STA. In addition, when outage delay present=1, the APapplies the ROM change during the next TXOP interval after the currentTXOP interval expires.

In still another example, time to apply an ROM change may vary dependingon whether the number of spatial streams and a receiving channelbandwidth are reduced or increased according to an ROM change request.

For example, when the STA makes an ROM request to increase the number ofspatial streams and a receiving channel bandwidth, the AP mayimmediately apply a changed ROM for a PPDU subsequently transmittedafter transmitting an ACK of the ROM request transmitted by the STA.That is, once the ACK of the current ROM request is transmitted, the APmay apply the changed ROM even in the current TXOP interval.

When the STA makes an ROM request to reduce the number of spatialstreams and a receiving channel bandwidth, the AP may apply the ROMchange during the next TXOP interval after the current TXOP intervalexpires.

Further, contrary to the previous example, when the STA makes an ROMrequest to reduce the number of spatial streams and a receiving channelbandwidth, the AP may immediately apply a changed ROM for a PPDUsubsequently transmitted after transmitting an ACK of the ROM requesttransmitted by the STA. When the STA successfully receives an ACK of theROM request, the ROM change may be applied in the next TXOP interval.When the STA fails to receive the ACK of the ROM request, the ROM changeis not applied even in the next TXOP interval.

In addition, when the STA makes an ROM request to increase the number ofspatial streams and the receive channel bandwidth, the AP may apply theROM change during the next TXOP interval after the current TXOP intervalexpires. That is, the AP may apply the ROM change in the next TXOPinterval regardless of whether the STA has received the ACK of the ROMrequest.

FIG. 24 is a flowchart illustrating a procedure for processing controlinformation for configuring a PPDU according to an embodiment.

First, terms used herein are defined as follows. A first STA maycorrespond to an AP STA, and a second STA may correspond to a non-AP STAthat performs communication with the AP STA.

In step S2410, the first STA receives, from a second STA, indicationinformation that indicates a change of an operating mode indicating thenumber of spatial streams and a receiving channel bandwidth supported bythe second STA during a transmission opportunity (TXOP) interval. Thatis, since the indication information that indicates the change of theoperating mode may correspond to a receive operating mode (ROM) request,the second STA makes an ROM change request to the first STA. Thereceiving channel bandwidth may include at least one of 20 MHz. 40 MHz,80 MHz, and 160 MHz.

In step S2420, when the number of spatial streams and the receivingchannel bandwidth are reduced, the first STA configures a PPDU for thesecond STA using the indication information after transmitting an ACK ofthe indication information. Further, when the number of spatial streamsand the receiving channel bandwidth are reduced, the PPDU for the secondSTA may be configured during the TXOP interval or a TXOP intervalsubsequent to the TXOP interval. That is, once the ACK of the ROMrequest is transmitted to the second STA, a changed ROM may be appliedeven in the current TXOP interval.

In step S2430, when the number of spatial streams and the receivingchannel bandwidth are increased, the first STA configures a PPDU for thesecond STA using the indication information during a TXOP intervalsubsequent to the TXOP interval. Further, when the number of spatialstreams and the receiving channel bandwidth are increased, the PPDU forthe second STA may be configured during the TXOP interval subsequent tothe TXOP interval regardless of transmitting the ACK of the indicationinformation.

The indication information may include an operating mode changeindicator bit. The operating mode change indicator bit may correspond toan ROM change indicator bit. The operating mode change indicator bit mayindicate a TXOP interval in which the PPDU for the second STA isconfigured. That is, an interval in which an ROM change is applied maybe identified on the basis of a value indicated by the operating modechange indicator bit.

The indication information may be included in a data field of a PPDUforwarded to the first STA. The data field of the PPDU forwarded to thefirst STA may correspond to a QoS data frame. Further, the indicationinformation may be included in a medium access control (MAC) header ofthe data field.

The indication information may indicate whether the second STA indicatesuplink multi-user MU) transmission, the number of receiving spatialstreams supported by the second STA, and the number of transmittingspatial streams supported by the second STA. That is, the indicationinformation may be used as information on a transmit operating mode whenthe second STA performs UL MU communication through a trigger frame.

FIG. 25 is a block view illustrating a wireless device to which theexemplary embodiment of the present invention can be applied.

Referring to FIG. 25, as an STA that can implement the above-describedexemplary embodiment, the wireless device may correspond to an AP or anon-AP STA. The wireless device may correspond to the above-describeduser or may correspond to a transmitting device transmitting a signal tothe user.

The AP 2500 includes a processor 2510, a memory 2520, and a radiofrequency (RF) unit 2530.

The RF unit 2530 is connected to the processor 2510, thereby beingcapable of transmitting and/or receiving radio signals.

The processor 2510 implements the functions, processes, and/or methodsproposed in the present invention. For example, the processor 2510 maybe implemented to perform the operations according to theabove-described exemplary embodiments of the present invention. Morespecifically, among the operations that are disclosed in the exemplaryembodiments of FIG. 1 to FIG. 24, the processor 2510 may perform theoperations that may be performed by the AP.

The non-AP STA 2550 includes a processor 2560, a memory 2570, and aradio frequency (RF) unit 2580.

The RF unit 2580 is connected to the processor 2560, thereby beingcapable of transmitting and/or receiving radio signals.

The processor 2560 implements the functions, processes, and/or methodsproposed in the present invention. For example, the processor 2560 maybe implemented to perform the operations of the non-AP STA according tothe above-described exemplary embodiments of the present invention. Theprocessor may perform the operations of the non-AP STA, which aredisclosed in the exemplary embodiments of FIG. 1 to FIG. 32.

The processor 2510 and 2560 may include an application-specificintegrated circuit (ASIC), another chip set, a logical circuit, a dataprocessing device, and/or a converter converting a baseband signal and aradio signal to and from one another. The memory 2520 and 2570 mayinclude a read-only memory (ROM), a random access memory (RAM), a flashmemory, a memory card, a storage medium, and/or another storage device.The RF unit 2530 and 2580 may include one or more antennas transmittingand/or receiving radio signals.

When the exemplary embodiment is implemented as software, theabove-described method may be implemented as a module (process,function, and so on) performing the above-described functions. Themodule may be stored in the memory 2520 and 2570 and may be executed bythe processor 2510 and 2560. The memory 2520 and 2570 may be locatedinside or outside of the processor 2510 and 2560 and may be connected tothe processor 2510 and 2560 through a diversity of well-known means.

What is claimed is:
 1. A method for configuring a physical layerprotocol data unit (PPDU) in a wireless local area network (WLAN)system, the method comprising: receiving, by a first station (STA),indication information on a change of an operating mode includinginformation on a number of spatial streams and a receiving channelbandwidth supported by a second STA from the second STA during atransmission opportunity (TXOP) interval; when the number of spatialstreams and the receiving channel bandwidth are reduced, configuring, bythe first STA, a PPDU for the second STA based on the indicationinformation after transmitting an acknowledgement (ACK) of theindication information; and when the number of spatial streams and thereceiving channel bandwidth are increased, configuring, by the firstSTA, the PPDU for the second STA based on the indication informationduring a second TXOP interval that is subsequent to the TXOP interval,wherein the PPDU for the second STA is configured during the second TXOPinterval regardless of transmitting the ACK of the indicationinformation.
 2. The method of claim 1, wherein when the number ofspatial streams and the receiving channel bandwidth are reduced, thePPDU for the second STA is configured during the TXOP interval or thesecond TXOP interval.
 3. The method of claim 1, wherein the indicationinformation comprises an operating mode change indicator bit, and theoperating mode change indicator bit includes information on a TXOPinterval in which the PPDU for the second STA is configured.
 4. Themethod of claim 1, wherein the indication information is comprised in adata field of a PPDU forwarded to the first STA.
 5. The method of claim4, wherein the indication information is comprised in a medium accesscontrol (MAC) header of the data field.
 6. The method of claim 1,wherein the indication information includes information on whether thesecond STA indicates uplink multi-user (UL MU) transmission, a number ofreceiving spatial streams supported by the second STA, and a number oftransmitting spatial streams supported by the second STA.
 7. The methodof claim 1, wherein the receiving channel bandwidth comprises at leastone of 20 MHz, 40 MHz, 80 MHz, or 160 MHz.
 8. The method of claim 1,wherein the first STA is an access point (AP) STA, and the second STA isa non-AP STA that performs communication with the AP STA.
 9. A firststation (STA) in a wireless local area network (WLAN) system, the firstSTA comprising: a radio frequency (RF) transceiver to transmit orreceive a radio signal; and a processor to control the RF transceiver,wherein the processor is configured to: receive indication informationon a change of an operating mode including information on a number ofspatial streams and a receiving channel bandwidth supported by a secondSTA from the second STA during a transmission opportunity (TXOP)interval; when the number of spatial streams and the receiving channelbandwidth are reduced, configure a PPDU for the second STA based on theindication information after transmitting an acknowledgement (ACK) ofthe indication information; and when the number of spatial streams andthe receiving channel bandwidth are increased, configure the PPDU forthe second STA using based on the indication information during a secondTXOP interval that is subsequent to the TXOP interval, wherein the PPDUfor the second STA is configured during the second TXOP intervalregardless of transmitting the ACK of the indication information.